1. Field of the invention
This invention relates to relief valves and more particularly to a collapsible pin relief valve for fluid systems of relatively large diameter.
In the past, I have successfully utilized a collapsible pin relief valve by utilizing Euler's law acting on a pin for monitoring pressure in a conductor generating a force up to approximately 8,000 pounds (3,600 kg) against the pin.
A collapsible pin in a two inch piston diameter pressure relief valve, connected with a conductor of the same size, containing 5,000 psi (2,250 kg) generates a force on the collapsible pin on the order of 15,000 pounds (6,750 kg). It is desirable to reduce this pin force without reducing the piston diameter.
There is a need for a valve to monitor such pressure in a large diameter, for example, a 24 inch (61 cm) conductor with a 24" piston opening, but this requires an unrealistically large diameter collapsible pin.
This invention solves this problem by providing a collapsible pin relief valve in which dual pistons of different diameter which partially balances out the force acting on the collapsible pin.
2. Description of the prior art
The most pertinent prior patent is believed to be my U.S. Pat. No. 5,012,834, issued May 7, 1991, for Fluid Pressure Flare Relief Valve.
This patent discloses a valve body connected with a fluid line in which the valve body is enlarged and provided with a lateral opening normally closed by a double wall valve head to form a valve head chamber laterally of a fluid passageway through the valve body.
The fluid passageway contains a box-like chamber having aligned bores in opposite walls normally closed by dual pistons secured to a piston rod projecting through the valve head chamber and through the closed end of a cylinder projecting into the valve head chamber and slidably supporting a smaller diameter pilot piston secured to the piston rod.
The outwardly projecting end of the piston rod supports one end of an excess fluid pressure collapsible pin supported at its other end by the end plate of a pin cage surrounding the collapsible pin and connected with the cylinder projecting out of the valve head chamber.
A spring urged poppet valve a admits upstream fluid pressure to the valve head chamber, so that excess pressure above a predetermined value against the pilot piston and the piston remote from the valve head chamber unbalances the pistons, collapsing the pin to release the excess pressure through the passageway downstream outlet.
This invention is distinctive over this patent by proving a valve housing with a flow passageway therethrough in which a guide piston is slidably mounted in the valve housing for movement toward and away from the passageway outlet port and is connected with one end of a hollow cylinder having a smaller diameter stop piston secured to its other end portion and closing the passageway outlet port of the valve body. A piston rod connected with the guide piston opposite the stop piston projects outwardly of the valve body and abuts one end of a collapsible pin supported at its other end by a pin cage means secured to the valve housing.
Fluid pressure in the valve housing acts on confronting surfaces of both pistons. Because of the area difference a major portion of the high pressure is balanced out. A pin holds the stop piston on seat while the force on the pin is proportional to upstream pressure. Excess pressure in the valve housing, beyond the pressure balanced rating of the collapsible pin forces both pistons toward the collapsible pin to collapse the latter and open the fluid passageway.